There are many known methods for reproducing spectacles in three-dimensional images so that an observer can have a full spatial impression thereof. This is done, e.g., by arranging two different images of an object, e.g., a "right-eye" image and a "left-eye" image, photographed from two different directions or angles as a viewer would see the object with his two eyes along the corresponding directions; and allowing the viewer to see the right-eye image and the left-eye image displayed on a screen in an alternating sequence through a pair of glasses operating in the same alternating sequence. One of such three dimensional viewing systems is described in U.S. Pat. No. 4,907,860 issued to Lowel A. Noble, "Three Dimensional Viewing Glasses". The Noble patent comprises a pair of three dimensional viewing glasses which are alternatingly turned on and off, and have lenses made of a liquid crystal material and a remote synchronization signalling system which transmits a control signal to change the on and off states in each of the lenses. The control signal is generated in synchronization with the alternating occurrences of the right-eye and left-eye images: that is, when such control signal is transmitted to the glasses, the right-eye and the left-eye images can be perceived by the observer's right and left eyes, respectively.
Similarly, for three dimensional viewing with a video cassette recorder("VCR"), a video source such as a video tape is employed to provide a sequence of video frames, each of which may be divided into two video fields corresponding to two different images that are recorded from a first and a second directions, respectively, in an alternating sequence. When the sequence of video frames is reproduced by the VCR, one of the two fields can be viewed as a right-eye image and the other as a left-eye image through the use of the three dimensional viewing glasses and the synchronization signalling system as described above.
It is, however, difficult to synchronize between the occurrences of the right-eye and left-eye images and the alternating on/off states of the lenses at an initial stage since the control signal is artificially produced by the remote synchronization signalling system. Therefore, if there is a poor synchronization, there will be a defective reproduction of a three dimensional imagery. Further, there is no way to change the alternating sequence between the right-eye and left-eye images when the right-eye image is displayed for viewing by the left eye and vice versa.